Double-exhaust gas-blast circuit breaker

ABSTRACT

A double-exhaust gas-blast circuit breaker comprises two spacedapart electrodes, a main flow channel leading past one electrode, and a vent passage leading past the other electrode. A blast valve located downstream from said one electrode controls flow through both the main flow channel and the vent passage. Control of flow through the vent passage by the blast valve is made possible by a tube of insulating material bridging the interelectrode gap, receiving flow at one end from the vent passageand exhausting into the main flow channel upstream of the blast valve. Cooling and filtering means between the vent passage and the insulating tube cools and filters the flow entering said tube.

United States Patent [1 1 Beatty,

[111 3,773,994 [451 NW. 2a, 1973 DOUBLE-EXHAUST GAS-BLAST CIRCUIT BREAKER [75] Inventor: John W. Beatty, Newton Square, Pa.

[73] Assignee: General Electric Company,

Philadelphia, Pa.

[22] Filed: June 30, 1972 [21] Appl. No.: 267,945

[52] U.S. Cl 200/148 B [51] Int. Cl. H01h 33/86 [58] Field of Search 200/148 B, 148 R [56] References Cited UNITED STATES PATENTS 3,418,440 12/1968 Beatty et a]. 200/148 B 3,480,751 11/1969 Frowein 200/148 B Primary Examiner-Robert S. Macon Attorney-J. Wesley Haubner et al.

[57] ABSTRACT A double-exhaust gas-blast circuit breaker comprises two spaced-apart electrodes, a main flow channel leading past one electrode, and a vent passage leading past the other electrode. A blast valve located downstream from said one electrode controls flow through both the main flow channel and the vent passage. Control of flow through the vent passage by the blast valve is made possible by a tube of insulating material bridging the inter-electrode gap, receiving flow at one end from the vent passage-and exhausting into the main flow channel upstream of the blast valve. Cooling and filtering means between the vent passage and the insulating tube cools and filters the flow entering said tube.

8 Claims, 5 Drawing Figures PAIENIEBunvzo ms 3 773; 994

sum 2 or 2 DOUBLE-EXHAUST GAS-BLAST CIRCUIT BREAKER BACKGROUND This invention relates to a gas-blast circuit breaker and, more particularly, to a gas-blast circuit breaker of the double-exhaust type.

In the type of circuit breaker that I am concerned with, there is a gap between two spaced electrodes disposed in pressurized gas. Across this gap and through a flow controlling nozzle disposed between the electrodes, an arc is drawn during a circuit interrupting operation. A normally-closed blast valve downstream of one electrode is opened during interruption to produce a flow of gas through the nozzle axially of the arc and past said one electrode. The purpose of this flow of gas is to cool the arc and scavenge the gap of arcing products so as to increase the rate at which dielectric strength is built up across the gap when the current zero point is reached. By increasing this rate of dielectric recovery, it is possible to improve the interrupting capacity of the circuit breaker.

it has been found that the interrupting capacity of such an axial-blast type of circuit breaker can be increased by providing a vent passage through the other of the electrodes, affording an auxiliary passage through which arcing products can be vented from the gap. Such a circuit breaker is referred to herein as a double-exhaust type circuit breaker. In U.S. Pat. No. 3,471,667-Barkan, assigned to the assignee of the present invention, flow through the auxiliary vent passage is controlled by a normally-closed auxiliary blast valve which is opened in response to a relatively high current during the interrupting operation. While this prior circuit breaker has many advantages, it is subject to the disadvantage that it is not well suited for interrupting the current produced by a so-called evolving fault. An evolving fault is one which develops while the circuit breaker is switching a relatively low current. The evolving fault produces an abrupt increase in current while the circuit breaker is passing through an intermediate point in its opening operation; and the currentresponsive auxiliary blast valve cannot always open rapidly enough in response to this abrupt current increase to enable the circuit breaker to adequately interrupt the fault-current.

It is possible to overcome this problem by opening the auxiliary blast valve each time the circuit-breaker is opened, as through a mechanical linkage tied to-the circuit-breaker operating mechanism; but this approach has some reliability problems because it is always possible that the repetitively-operated auxiliary valve will not seat properly, thus producing undesirable leakage. Moreover, the more valves that are present, the more chance there is for undesirable leakage or for a valve-malfunction.

SUMMARY An object of my invention is to provide a doubleexhaust circuit breaker which has improved-ability to handle high current faults, even if they are of the evolving type, and which has no auxiliary blast valve which could be a source of reliability or leakage problems.

Another object is to construct a double-exhaust circuit breaker in such a manner that a main blast valve located downstream from the electrodes can control both the main blast through the nozzle of the interrupter and the auxiliary blast through one of the electrodes.

Another object is to pneumatically interconnect the auxiliary vent passage and the main exhaust passage by means capable of withstanding the voltage present between the electrodes and capable of indefinitely retaining this capability despite the passage therethrough of the auxiliary blast from the arcing gap.

In carrying out my invention in one form, I provide a main exhaust channel leading past one electrode and a vent passage leading past the other electrode. A blast valve located downstream from said one electrode controls flow through the main flow channel. A tube of insulating material bridges the interelectrode gap, receives flow at one end from the vent passage, and exhausts such flow at its opposite end into the main flow channel at a point upstream from the blast valve. Cooling and filtering means between the vent passage and the insulating tube cools and filters the flow entering said tube, thereby protecting the tube against dielectric impairment.

BRIEF DESCRIPTION OF DRAWINGS For a better understanding of the invention, reference may be had to the following description taken in conjunction with the accompanying drawings, wherein:

FIG. 1 is a sectional view through a circuit interrupter embodying one form of the invention.

FIG. 2 is a sectional view along the line 2--2 of FIG. 1.

FIG. 3 is an enlarged sectional view through a portion of FIG. 1, specifically, through the check valve at the mouth of the auxiliary blast passage 95, 96.

FIG. 4 is an enlarged sectional view of a portion of a modified form of the invention.

FIG. 5 is a diagrammatic plan view of an interrupter embodying another modified form of the invention;

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT Referring now to FIG. 1, the circuit interrupter shown therein is of the sustained-pressure, gas-blast type described and claimed in US. Pat. No. 2,783,338- Beatty, assigned to the assignee of the present invention. Only those parts of the interrupter that are considered necessary to provide an understanding of the present invention have been shownin FIG. I. In this respect, only the right hand portion of the interrupter has been shown in section inasmuch as the interrupter is generally symmetrical with respect to a vertical plane and the left hand portion is substantially identical to the right hand portion. As described in detail in the abovementioned Beatty patent, the interrupter comprises a casing 12 which is normally filled with pressurized gas to define an interrupting chamber 11. Located within the interrupting chamber 11 are a pair of relatively movable contacts 14 and 16 which can be separated to draw an arc within the pressurized gas within the chamber 11. The contact 14 is relatively stationary, whereas the other contact 16 is mounted for pivotal motion about a fixed, current-carrying pivot 18. Stationary contact 14 is mounted on the inner end of a high voltage terminal bushing 7 comprising two porcelain shells 8 and 8a and a conductive stud 9 extending there-' through. When movable contact 16 is driven clockwise about pivot 18 from its solid-line closed position of 7 FIG. 1, an arc is established in the region where the contacts part. The movable contact 16 is shown by dotted lines in FIG. 1 in a partially-open position through which it passes during a circuit-interrupting operation after having established an arc.

Movable contact 16 is supported by means of its current-carrying pivot 18 on a conductive bracket 19 that is preferably formed integral with a stationary clyinder 32. Cylinder 32 at its lower end is suitably supported from a generally cylindrical casting 33. Casting 33 at its lower end is suitably secured to a flange 35 rigidly carried by the stationary metallic casing 12.

For producing a gas blast to aid in extinguisihing the arc, cylindrical casting 33 contains a normally-closed main exhaust channel 36 leading from the interrupting chamber 11 to the surrounding atmosphere. Casting 33 at its upper end is provided with a tubular nozzle member 38 having an orifice portion 39 at its outer end defining an inlet 37 to the main exhaust channel 36. This inlet 37 is referred to hereinafter as the orifice opening. The flow of arc-extinguishing gas through tubular nozzle 38 and exhaust channel 36 is controlled by means of a cylindrically-shaped reciprocable blast valve member 40 located at the outer, or lower, end of exhaust channel 36. This blast valve member 40 normally occupies a solid-line, closed position wherein a portion 42 at its lower end sealingly abuts against a stationary valve seat 34 carried by exhaust casting 33.

During a circuit-interrupting operation, movable blast valve member 40 is driven upwardly from its solid-line, closed position of FIG. 1 through a partially open intermediate position shown in dotted lines in FIG. 1. Opening of valve member 40 allows pressurized gas in the chamber 11 to flow at high speed through orifice opening 37 and nozzle 38 and out exhaust channel 36 past valve member 40 to atmosphere, as indicated by the dotted line arrows B of FIG. 1 The manner in which the gas blast acts to extinguish the arc will soon be described in greater detail.

At its upper end, the cylindrical blast valve member 40 surrounds a projecting cylindrical support 41 upon which the valve member 40 is smoothly slidable. The support 41 is fixed to the casting 33 by suitable means (not shown). A suitable compression spring (not shown) positioned between the movable valve member 40 and the lower end of support 41 tends to hold the valve member 40 in its closed position against the valve seat 34.

To protect support 41 and the upper end of valve member 40 from the harmful effects of arcing, a protective metallic tube 43 is positioned about these parts and is suitably secured to support 41. Secured to the outer surface of this tube is a downstream probe or electrode 45, preferably of a refractory metal, which projects radially from tube 43 and transversely into the path of the gas blast flowing through channel 36. As will soon appear more clearly, the downstream terminal of the arc is transferred to this electrode 45 during an interrupting operation and, after such transfer, occupies an instantaneous position generally corresponding to that shown at 46. The downstream electrode is preferably constructed as shown and claimed in U.S. Pat. No. 2,897,324-Schneider, assigned to the assignee of the present invention, so that it has a non-streamlined upstream surface 48 that coacts with the gas blast to form a stagnation region upstream from the surface 48. The terminal of an are such as 46 reaching the electrode 45 is captured within the stagnation region and thus prevented from being driven further downstream by the gas blast.

For controlling the operation of movable blast valve 40 and movable contact 16, a combined operating mechanism 50 is provided. This mechanism 50 is preferably constructed in the manner disclosed and claimed in the aforementioned Beatty U.S. Pat. No.

2,783,338, and its details form no part of the present invention. Generally speaking, this mechanism 50 comprises a blast valve-controlling piston 51 and a contactcontrolling piston 52 mounted within the cylinder 32. Blast valve-controlling piston 51 is coupled to movable blast valve member 40 through a piston rod 54 suitably clamped to valve member 40. The contact-controlling piston 52, on the other hand, is connected to the movable contact 16 through a piston rod 58 and a cross head 59 secured to the piston rod. A link 60 pivotally joined to the cross head 59 at 61 and to movable contact 16 at 62 interconnects cross head 59 and movable contact 16. When blast valve-controlling piston 51 is driven upwardly, it acts to open blast valve member 40, and, simultaneously, to drive contact-controlling piston 52 upwardly to produce opening movement of the movable contact member 16.

Opening movement of contact member 16 first establishes an are between the ends of the contacts 14 and 16. Shortly thereafter, however, the blast of gas which has been flowing through the orifice opening 37, as indicated by the dotted-line arrows B, forces the upstream terminal of the are on to an upstream arcing electrode 7 0, which is electrically connected to the stationary contact 14. As opening motion of movable contact 16 continues, the gasblast forces the downstream terminal of the arc to transfer from the movable contact 16 to orifice structure 39, which is electrically connected to the movable contact 16. The gas blast then impels the downstream terminal of the are through the orifice opening 37 and nozzle 38 on to the upper end of the protective metallic tube 43. From there, the gas blast drives the downstream arc terminal downwardly and into the previously-described stagnation region adjacent the upstream surface 48 of the electrode 45. The are then occupies the position generally shown at 46. When the arcis in this position, the arc column extends through the orifice opening 37 and is subjectedto the cooling and deionizing effect of the axial blast. After completion of the interrupting operation, the blast valve 40 is returned to its closed position of FIG. 1 by the operating mechanism 50 while the contacts 14, 16 remain open.

It has been found that the current-interrupting capacity of a circuit breaker constructed as above described can be increased by directing an auxiliary blast from the arcing region through the upstream electrode during the circuit-interrupting operation. For accommodating this auxiliary blast, I provide an auxiliary blast passage 95, 96 leading through the upstream electrode and through an insulating tube 100 that bridges the gap between the spaced electrodes 45 and 70. The portion of this auxiliary blast passage that extends through electrode 70 is designated 95, and the portion extending through insulating tube 100 is designated 96.

Connected in this flow passage 95, 96 is a device which acts to cool and filter the auxiliary blast before it enters the insulating tube 100. The cooling device 105 comprises a casing 108, preferably of a highlyconductive material such as copper. Casing 108 comprises a cylindrical portion 110 and spaced-apart end walls 112 and 114. End wall 112 is suitably secured to electrode structure 70 and end wall 114 to the end flange 116 of the terminal bushing 7. Electric current can flow between stud 9 of the terminal bushing and the electrode structure 70 via the conductive casing 108.

As illustrated by the dotted-line arrows 117, the auxiliary blast enters the cooling device 105 through a central opening 120 in end wall 112 and exhausts there from via a radially-extending outlet 121, following which it flows through insulating tube 100 into the main exhaust channel 36 as indicated by the arrows 118. lnterposed between the inlet 120 and outlet 121 of device 105 is cooling structure in the form of two concentric cylinders of metal screening 124 and 125.

Each cylinder of screening comprises a plurality of concentric layers. The outer cylinder 124 has a smaller mesh than the inner cylinder 125. Because of their large surface areas, these screens effectively extract heat from the hot gases passing therethrough, thus very substantially reducing the temperature of the gases and effectively suppressing flame emission into the space 126 surrounding the screens. Space 126 may be thought of as an annular exhaust manifold that collects the exhaust gases and conveys them to outlet 121.

There is a tendency for gas flow through the screens 124, 125 to concentrate in the region generally aligned with outlet 121, thus causing local burning of the screens. To divide the flow more uniformly, a plurality of radiallyextending vanes 127 are provided within the bore 123 of inner screen cylinder 125. As shown in FIG. 2, these wines 127 extend radially outward from the center of the bore into contact with the inner screen cylinder 125, thus forcing the gas in any given sector between the vanes to enter the screen cylinder in a region alinged with that sector. The result is a more complete utilization of the screening to provide more effective cooling and to suppress burning of the screening in the region aligned with outlet 121.

Since the gases entering the tube 100 are relatively cool after having passed through cooler 105, their dielectric strength is much higher than it would otherwise be, and there is thus much less chance for a flashover to occur through them while they are traveling through the tube 100 across the gap between the electrodes.

The screens 124, 125 also act as a filter which helps to filter out hot conductive particles entrained in the auxiliary blast. These particles, if they remain in the blast, not only tend to reduce the dielectric strength of the gas but also tend to deposite on the inner wall of tube 100, thus impairing the dielectric strength of the tube.

To aid in filtering out and trapping these particles, a trap 128 is provided. This trap comprises a tubular body 129 having a central chamber 130 aligned with bore 123 of screening cylinder 125. Between central chamber 130 and the bore 123 are several disks 132 of coarse, large mesh screening through which particles entrained in the air can pass relatively freely. Behind the screening disk 132 is a mass of loose metal mesh I33 forming a labyrinth-like structure with extensive exposed surfaces. While most of the gases flow radially outward as shown by arrows 117, the heavy particles therein tend to continue in a straight line path through the bore 123 into the chamber 130, where they are trapped in the labyrinth structure 133. Trapping these particles in this region out of the main flow path prevents these particles from accumulating in and clogging the screening cylinders 124, through which the main flow passes.

For supporting the vanes 127, a stud 135, suitably joined to the vans is provided. This stud 135 extends through the chamber 130 and is supported on an end member 136. When a nut 137 on the outer end of stud 136 is tightened, the vanes are clamped against the screening disks 132 which are thus sandwiched between the vanes and a shoulder on body 129.

The insulating tube 100 has an outlet which communicates with the main exhaust channel 36 in casting 33 through a port 138 a short distance upstream from the seat 34 of the blast valve member 40. When blast valve member 40 is opened during the interrupting operation, as above-described, high pressure air from the interrupter chamber flows past the valve 40 via the auxiliary blast passage 95, 96 to create the above-described auxiliary blast. This, of course, is in addition to the main blast flowing through nozzle 38 and the main exhaust channel 36.

Since the main blast passing through channel 36 comprises ionized gases containing conductive particles resulting from arcing, it is important that such blast be excluded from the insulating tube 100 in order to avoid any dielectric impairment thereof. To prevent any significant portion of the main blast from entering the insulating tube 100, I provide at the outlet end of the exhaust blast passage 95, 96 a check valve 140 which allows flow through passage 95, 96 only in the direction of arrows 118.

Check valve 140 can be of any suitable conventional design, one form of which is shown in detail in FIG. 3. This check valve of FIG. 3 comprises a cylindrical casing 142, a spider 143 fixed therein with openings 144 extending therethrough, a movable valve member 145 for controlling flow through openings 144. A central mounting rod 146 fixed to movable valve member 145 supports the valve member for horizontal movement with respect to spider 143. A compression spring 148 biases movable valve member 145 into its illustrated normally-closed position against the spider. When the pressure to the right of valve member 145 exceeds that to the left by a predetermined amount, it forces valve member 145 away from the spider, opening passages 144 to permit gas to flow therethrough from right to left. If the pressure to the left of the movable valve member (i.e., the pressure in the main exhaust channel 36) should equal or exceed that to the right, the valve member 145 would close and block flow from left to right.

In a modified form of the invention, I eliminate the check valve 140 and use instead a cooler and filter 150 (FIG. 4) similar to the device 105 at the inlet to insulating tube 100. This cooler and filter comprises a cylindrical casing 152 and a partition 154 fixed therein and having flow passages 156 therethrough. At one side of the partition are two concentric cylinders 158 and 160 of screening. Surrounding the outer cylinder 158 is a manifold space 162 communicating with flow passages 156. The auxiliary blast entes via tube 100, passing through flow passages 156 and then radially inward through screens 158 and 160, exiting through an outlet 164. Any gas tending to flow in the opposite direction (i.e., from main exhaust channel 36 into tube 100) must flow radially outward through the screening cylinders 160, 158, and this cools and filters such gas thereby increasing its dielectric strength and reducing the likelihood that it will break down while in tube 100 or will impair the insulating properties of tube 100.

FIG. 1 shows the insulating tube 100 communicating with the main exhaust channel 36, which is of annular form, through a port 138 that is generally aligned with downstram electrode 45. In a preferred form of my invention, however, I locate this exhaust port 138 in a position within annular exhaust channel 36 that is displaced 90 from the electrode 45 and the nozzle opening 37, as is illustrated in FIG. 5. Locating exhaust port 138 in this displaced position is advantageous because very little of the hot arcing products entrained in the main blast ever enter this displaced region. These hot arcing products (in passing through exhaust channel 36 and past the blast valve 40) are confined almost entirely to the region generally aligned with the downstream electrode 45 and the nozzle opening 37. Thus, with the exhaust port 138 located in the displaced position of FIG. 5, there is little tendency of the hot arcing products to enter the insulating tube 100 from the exhaust channel 36. This enables me to eliminate the check valve 14 of FIG. 3 with little risk of insulation impairment from back-flowing gas. Preferably, a cooler and filter such as 150 of FIG. 4 is provided adjacent exhaust port 138 to give extra assurance that any backflowing gas entering tube 100 will be dielectrically strong and clean. In some circuit breakers, even this device 150 can be omitted, if the exhaust portions 138 are displaced as shown in FIG. 5.

It is to be noted in FIG. 5 that two insulating tubes 100 are provided for the auxiliary blasts. One of these provides for an auxiliary blast for the break at the left of the central casting 33 and the other provides for an auxiliary blast for the break at the right of the central casting. Each of these insulating tubes 100 exhausts into annular channel 36 through an outlet port 138 in the central casting 33. Within annular channel 36 these outlet ports 138 are displaced from each other by approximately l80and from the nozzle openings 37 by approximately 90thus providing maximum angular spacing from the nozzle openings and the main electrodes 45.

One of the objects of this invention is to provide a double-exhaust circuit breaker that has improved ability to handle an evolving type fault, i.e., one which develops while the circuit breaker is switching a relatively low current. If a separate current-responsive auxiliary blast valve is provided, it is not always possible to open the separate valve rapidly enough to produce the auxiliary blast in response to the abrupt increase in current produced by the evolving fault. This is no problem in my circuit breaker because the auxiliary blast would already be present should an evolving fault develop since the main blast valve, which is the only valve involved, would then already to be open.

While it is possible to provide an auxiliary blast valve that is opened each time the circuit breaker is opened, this approach, as pointed out hereinabove, has some reliability problems because of the increased possibilities of valve-malfunction and undesirable leakage through the auxiliary blast valve when extra blast valves are present.

My circuit breaker requires no extra blast valves since I utilize the same blast valve (40) for controlling both the main and the auxiliary blast. It is to be further noted that this one blast valve controls the main and the auxiliary blasts not just for one break but for the two series-connected breaks at opposite sides of the central casting 33. 5 While I have shown and described a particular embodiment of my invention, it will be obvious to those skilled in the art that various changes and modifications may be made without departing from my invention in its broader aspects; and I, therefore, intend herein to cover all such changes and modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

l. A gas-blast circuit breaker comprising:

a. a pair of electrodes having a spaced-apart position with a gap therebetween across which an arc is drawn during a circuit-interrupting operation,

b. a nozzle having a flow passage through which said arc extends during said interrupting operation,

0. a housing adapted to contain pressurized gas in which said electrodes are disposed,

d. a main exhaust channel communicating with said nozzle flow passage,

e. a normally-closed blast valve at the outlet of said channel openable to produce a flow of gas through said nozzle and said channel and past one of said electrodes during said interrupting operation,

f. said blast valve being located downstream of said one electrode with respect to gas flow through said nozzle and channel,

g. a vent passage through the other of said electrodes for venting from said gap arcing products in the region of the other of said electrodes,

h. a tube of insulating material communicating with said vent passage and bridging said gap for conveying across said gap the How through said vent passage,

i. means forming an exhaust port for the flow through said tube of insulating material,

j. said exhaust port being located at a point within said main exhaust channel upstream from said blast valve so that flow through said vent passage and said tube are controlled by said blast valve,

k. and cooling and filtering means between said vent passage and said tube for cooling and filtering the flow entering said tube.

2. A circuit breaker as defined'in claim 1 and further comprising a check valve between said exhaust port and said tube for blocking flow from said main exhaust channel into said tube but allowing flow in the opposite direction.

3. The circuit breaker of claim 1 in which:

a. said main exhaust channel has a portion generally aligned with said one electrode relative to the main flow therethrough through which most of the hot arcing products carried past said one electrode travel, and

b. considered relative to the direction of main flow through said main exhaust channel, said exhasut port is located in a position spaced transversely of said exhaust channel from said portion generally aligned with said one electrode, thereby reducing the likelihood of hot arcing products entering said tube from said exhaust channel.

4. A circuit breaker as defined in claim 1 and further comprising second cooling and filtering means between said exhaust port and said tube for cooling and filtering any flow from said main exhaust channel into said tube. 5. The circuit breaker of claim 3 in combination with cooling and filtering means between said exhaust port and said insulating tube for cooling and filtering any flow from said main exhaust channel into said tube.

6. A gas-blast circuit breaker as defined in claim 1 and further comprising:

a. a second pair of electrodes within said housing having a spaced-apart position with a second gap therebetween across which a second arc is drawn during a circuit-interrupting operation,

b. said main exhaust channel communicating with said second gap,

c. said blast valve upon opening producing a flow of gas past one of the electrodes of said second pair and through said main exhaust channel,

d. said blast valve being located downstream of said one electrode of said second pair with respect to gas flow past said one electrode,

e. a second vent passage through the other of said electrodes of said second pair for venting arcing products from said second gap,

f. a second tube of insulating material communicating with said second vent passage and bridging said second gap for conveying across said second gap the flow through said second vent passage,

g. means forming a second exhaust port at said main exhaust channel for the flow that has passed from said second vent passage through said second tube of insulating material,

h. said second exhaust port being located upstream from said blast valve so that flow through said second vent passage and said second tube are controlled by said blast valve,

i. cooling and filtering means between said second vent passage and said second tube for cooling and filtering the flow entering said second tube.

7. The gas-blast circuit breaker of claim 6 in which:

a. said main exhaust channel is of a generally annular form and has two portions angularly displaced about said annulus by approximately 180 from each other and respectively aligned with said one electrode of each gap,

b. said exhaust ports are angularly displaced about said annulus by approximately lfrom each other and are located in positions angularly spaced by approximately from said two portions.

8. A gas-blast circuit breaker as defined in claim 1 in which said cooling and filtering means comprises: a housing having an inlet, perforated cylindrical cooling structure disposed within said housing and including a bore communicating with said inlet, a chamber within said housing surrounding said perforated structure for receiving gases flowing from said bore radially outwardly through said perforated structure, an outlet from said chamber communicating with said tube, and

means comprising vanes within said bore dividing said bore into discrete sections for receiving the gas entering through said inlet and distributing the radial flow through said cylindrical cooling structure more uniformly about its periphery. 

1. A gas-blast circuit breaker comprising: a. a pair of electrodes having a spaced-apart position with a gap therebetween across which an arc is drawn during a circuitinterrupting operation, b. a nozzle having a flow passage through which said arc extends during said interrupting operation, c. a housing adapted to contain pressurized gas in which said electrodes are disposed, d. a main exhaust channel communicating with said nozzle flow passage, e. a normally-closed blast valve at the outlet of said channel openable to produce a flow of gas through said nozzle and said channel and past one of said electrodes during said interrupting operation, f. said blast valve being located downstream of said one electrode with respect to gas flow through said nozzle and channel, g. a vent passage through the other of said electrodes for venting from said gap arcing products in the region of the other of said electrodes, h. a tube of insulating material communicating with said vent passage and bridging said gap for conveying across said gap the flow through said vent passage, i. means forming an exhaust port for the flow through said tube of insulating material, j. said exhaust port being located at a point within said main exhaust channel upstream from said blast valve so that flow through said vent passage and said tube are controlled by said blast valve, k. and cooling and filtering means between said vent passage and said tube for cooling and filtering the flow entering said tube.
 2. A circuit breaker as defined in claim 1 and further comprising a check valve between said exhaust port and said tube for blocking flow from said main exhaust channel into said tube but allowing flow in the opposite direction.
 3. The circuit breaker of claim 1 in which: a. said main exhaust channel has a portion generally aligned with said one electrode relative to the main flow therethrough through which most of the hot arcing products carried past said one electrode travel, and b. considered relative to the direction of main flow thrOugh said main exhaust channel, said exhasut port is located in a position spaced transversely of said exhaust channel from said portion generally aligned with said one electrode, thereby reducing the likelihood of hot arcing products entering said tube from said exhaust channel.
 4. A circuit breaker as defined in claim 1 and further comprising second cooling and filtering means between said exhaust port and said tube for cooling and filtering any flow from said main exhaust channel into said tube.
 5. The circuit breaker of claim 3 in combination with cooling and filtering means between said exhaust port and said insulating tube for cooling and filtering any flow from said main exhaust channel into said tube.
 6. A gas-blast circuit breaker as defined in claim 1 and further comprising: a. a second pair of electrodes within said housing having a spaced-apart position with a second gap therebetween across which a second arc is drawn during a circuit-interrupting operation, b. said main exhaust channel communicating with said second gap, c. said blast valve upon opening producing a flow of gas past one of the electrodes of said second pair and through said main exhaust channel, d. said blast valve being located downstream of said one electrode of said second pair with respect to gas flow past said one electrode, e. a second vent passage through the other of said electrodes of said second pair for venting arcing products from said second gap, f. a second tube of insulating material communicating with said second vent passage and bridging said second gap for conveying across said second gap the flow through said second vent passage, g. means forming a second exhaust port at said main exhaust channel for the flow that has passed from said second vent passage through said second tube of insulating material, h. said second exhaust port being located upstream from said blast valve so that flow through said second vent passage and said second tube are controlled by said blast valve, i. cooling and filtering means between said second vent passage and said second tube for cooling and filtering the flow entering said second tube.
 7. The gas-blast circuit breaker of claim 6 in which: a. said main exhaust channel is of a generally annular form and has two portions angularly displaced about said annulus by approximately 180* from each other and respectively aligned with said one electrode of each gap, b. said exhaust ports are angularly displaced about said annulus by approximately 180*from each other and are located in positions angularly spaced by approximately 90* from said two portions.
 8. A gas-blast circuit breaker as defined in claim 1 in which said cooling and filtering means comprises: a housing having an inlet, perforated cylindrical cooling structure disposed within said housing and including a bore communicating with said inlet, a chamber within said housing surrounding said perforated structure for receiving gases flowing from said bore radially outwardly through said perforated structure, an outlet from said chamber communicating with said tube, and means comprising vanes within said bore dividing said bore into discrete sections for receiving the gas entering through said inlet and distributing the radial flow through said cylindrical cooling structure more uniformly about its periphery. 